Wireless communication devices such as radiotelephones sometimes use two antenna systems with two or more antennas to transmit and receive radio frequency signals. In a radiotelephone using two diversity antennas, the second antenna should have comparable performance with respect to the first antenna, and the second antenna should also have sufficient de-correlation with respect to the first antenna so that performance improvements offered by diversity operation in multi-path propagation environments can be realized.
Diversity antenna system performance is a combination of many parameters. Sufficient operating frequency bandwidth(s), high radiation efficiency, desirable radiation pattern characteristic(s), and low correlation between diversity antennas are all desired components of diversity antenna system performance. Correlation is computed as the normalized covariance of the radiation patterns of two antennas. Due to the dimensions and generally-accepted placement of a main antenna along a major axis or a minor axis of a device such as a hand-held radiotelephone, however, efficiency and de-correlation goals are extremely difficult to achieve simultaneously.
Thus, there is an opportunity to continue to develop antenna structures that have broad operating frequency bandwidth(s), good radiation efficiency, and/or low-correlation radiation patterns. The various aspects, features, and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Drawings and accompanying Detailed Description.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.